DESCRIPTION OF SPATIAL PATTERN IN SEABIRD DISTRIBUTIONS ALONG LINE TRANSECTS USING NEIGHBOR-K STATISTICS

Description of spatial pattern is an important step towards understand ing the underlying, pattern-generating processes, but few statistical techniques adequately describe both the grain and intensity of a spati al distribution. Counts of seabirds collected along line transects are particularly problematic because the data may contain a high proporti on of zero counts, and the pattern at increased spatial scales is depe ndent on how the counts are grouped. Statistics based on Ripley's K fu nction seem well-suited to characterising scale-dependent spatial stru cture in such data. The spatial distributions of seabirds and fish sch ools off the Otago Peninsula, New Zealand, are described to illustrate the application of these statistics. Aggregation characteristics of s ooty shearwaters Puffinus griseus, red-and black-billed gulls Larus no vaehollandiae and L. bulleri and black-backed gulls L. dominicanus wer e similar. Sitting seabirds were highly clustered, with patch lengths between 145 and 2850 m. The distributions of flying seabirds were less crowded, with patch lengths from 135 to 5290 m. Patches of krill-eati ng red-and black-billed gulls were longer along transects with high sa linity structure. This may reflect a change in foraging strategy in re sponse to visible surface fronts. There was no clear association betwe en the distribution of sitting birds and the presence of schools of pr edatory, pelagic fish.